Method of fiberizing magnesium



METHOD OF FIBERIZING MAGNESIUM Thomas E. Leontis, Midland, and John F. Pashak, Linwood, Mich., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Original application September 16, 1949, Serial No. 116,214, now Patent No. 2,657,796, dated November 3, 1953. Divided and this application September 11, 1953, Serial No. 379,732

2 Claims. (Cl. 207-10) The invention relates to fiberized magnesium and magnesium-base alloys. It more particularly concerns a method of fiberizing magnesium and its alloys.

Insofar as we are aware, no method is commercially available by which magnesium and the magnesium-base alloys may be fiberized. Accordingly, the principal object of the invention is to provide a fiberized form of magnesium and its alloys. Another object is to provide a method of making a fiberized form of these metals.

The invention is based upon the discovery that by mixing together pellets of the metal to be fiberized with cupric acetate (Cu(C2H3O2)2.H2O), and die-expressing the mixture from a container through a die opening having a cross-sectional area which is about 1 to 10 per cent of that of the container, the metal exudes from the die as a bundle of thin metal strands encased in a thin sheath of metal. The strands are easily separable from each other and the sheath as individual metal fibers generally about 0.001 to 0.003 inch thick which exhibit a high tensile strength making them useful as fibrous fillers, as for example for rubber reinforcement and the like. In addition, the small diameter of the individual fibers gives them a large ratio of surface area to weight. This feature renders the fiberized metal especially useful in flashlight work, for example, where the ability of this material to oxidize rapidly may be advantageously utilized.

In carrying out the invention, magnesium or any of the magnesium-base alloys may be used in which the magnesium content exceeds about 75 per cent that are capable of being die-expressed as in extrusion. The metal is comminuted or pelleted in any convenient manner as by melting the metal and dropping the molten metal through a shot tower, by atomizing, or by machining. Particle size does not appear to be sharply critical. A convenient size is about 28 mesh. It is preferable to use a mixture of the metal particles of various sizes rather than a single mesh size.

The cupric acetate, with which the metal particles are mixed prior to die-expressing the mixture, is preferably comminuted to about the same mesh or sieve analysis as that of the metal particles. The amount to use is between about I to 20 per cent by weight of the mixture, 5 per cent being generally preferred.

The die-expression operation of the mixture is carried out at the elevated temperatures at which magnesium and its alloys are capable of plastic deformation such as from about 525 to 850 F., the lower temperatures of the die-expressing temperature range are in general preferable as these avoid the danger, present at the higher temperatures of the range, of the fibers becommg welded together during the extrusion and thus losing their individuality.

occur. Many of the magnesium-base alloys are satis- In addition, hot shortness may 2,701,636 Patented Feb. 8, 1955 factorily extruded at about 500 to 625 F. The temperature to use in the die-expressing step is limited on the lower end of the temperature range by the ability to supply the pressure required for die-expressing the metal, and on the upper end of the temperature range by the tendency for the fibrous nature .of the extrusion product to be lost by the welding effect of the higher die-expressing temperatures. Thus the upper limit of temperature is generally somewhat lower (e. g. 25 to Fahrenheit degrees) than that which would be satisfactory for a conventional extrusion of the same alloy alone. These temperatures are usually between about 525 and 850 F., although temperatures between about 500 and 600 F. are preferable.

1 Example 1 Commercial magnesium comminuted to a mesh size between about 20 and 35 mesh was uniformly mixed with 5 per cent by weight of cupric acetate. The mixture was loaded into a 3-inch diameter cylindrical eontainer of an extrusion press having a die opening 0.75 inch in diameter. The container was heated to between 550 F. and 570 F. The charge heated by the container was extruded through the die with a ram pressure starting at 215 tons and declining to tons as the extrusion proceeded. The die temperature increased from 540 F. at the beginning of the extrusion to 575 F. at the end. The metal extruded as a bundle of individual fibers about 0.001 to 0.003 inch in diameter and varying lengths of a few inches encased in a sheath about 0.06 inch thick. The individual fibers were easily separated from the bundle by hand.

Example 2 A magnesium-base alloy having a nominal composition of 3 per cent A1, 0.3 per cent Mn, and 1 per cent Zn, the balance being magnesium was comminuted to a mesh size between '2-4 and 28, mixed with 5 per cent by weight of cupric acetate, and extruded from a 3-inch diameter cylindrical container through a die 0.5 inch in diameter. The temperature of the container was about 550 F. and the die 520 F. at the beginning of the extrusion increasing to 590 F. at the end. The metal mixture extruded into a bundle of individual fibers about 2 to 3 inches long encased' in a sheath about 0.06 inch thick. The fibers were easily separated from each other by hand.

-' Example 3 In a similar test to that of Example 2 except that the die opening was 0.11 inch in diameter, the fiberized magnesium alloy obtained was heat-treated for 1 hour at 750 F. The tensile strength of the heat-treated fiberized product was 13,900 pounds per square inch with an elongation of 2 per cent in 2 inches.

This application is a division of our copending application Serial No. 116,214, filed September 16, 1949, now Patent No. 2,657,796, granted Nov. 3, 1953.

We claim:

1. The method of producing a bundle of easily separable fibers of magnesium and alloys thereof which comprises mixing together in comminuted form the metal and about 1 to 20 per cent by weight of cupric acetate, and die expressing the mixture at a temperature between about 500 and 800 F.

2. The method according to claim 1 in which the temperature is between about 550 and 570 F.

No references cited. 

1. THE METHOD OF PRODUCING A BUNDLE OF EASILY SEPARABLE FIBERS OF MAGNESIUM AND ALLOYS THEREOF WHICH COMPRISES MIXING TOGETHER IN COMMINUTED FORM THE METAL AND ABOUT 1 TO 20 PER CENT BY WEIGHT OF CUPRIC ACETATE, AND DIE EXPRESSING THE MIXTURE AT A TEMPERATURE BETWEEN ABOUT 500* AND 800* F. 